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371
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Introduction
Vikram Pakrashi currently works at the School of Mechanical and Materials Engineering, University College Dublin.
Additional affiliations
October 2010 - present
Publications
Publications (371)
This article presents the implementation of the canonical Lemaitre and Gurson–Tvergaard–Needleman (GTN) damage models and a more recent phase‐field type model within a Lagrangian, geometrically nonlinear, cell‐centred finite volume framework. The proposed segregated solution procedure uses Picard‐type defect (deferred) outer corrections, where the...
The effects of a rigid barrier on the stability of the structure while it is undergoing phase-locked motions due to the surrounding fluid–structure interactions, are studied. The primary structure and the near wake dynamics are modeled as a harmonic oscillator and a Van der Pol oscillator, respectively, and are weakly coupled via acceleration coupl...
Understanding the seismic response of pile supported structures during an earthquake is key to the design of resilient infrastructure. Kinematic soil-pile interaction is known to cause considerable alteration to the Foundation Input Motion experienced by a pile supported superstructure. Although soil-pile interaction has been rigorously investigate...
Citation: Ambrożkiewicz, B.; Czyż, Z.; Pakrashi, V.; Anczarski, J.; Stączek, P.; Koszewnik, A.; Wendeker, M.; Litak, G. Performance Assessment of a Piezoelectric Vibration Energy Harvester for Hybrid Excitation with Varying Cross Sections. Sensors 2024, 24, 7629. https://doi. Abstract: This paper experimentally examines the influence of hybrid exci...
An area noise survey and noise perception survey were conducted to qualify and quantify the typical noise sources and noise levels in NICU 1. A series of WBV measurements were conducted in line with ISO 2631:1997 on incubators and the various activities associated with their function. Noise and WBV results were compared to the relevant occupational...
There are several factors to account for marine growth including but not limited to temperature, salinity, chlorophyll-a content, existing species in the environment and predating. This paper proposes a model of biological growth for hard species on marine structures, which can be compatible with site-specific and realistic ecology while also being...
This paper proposes a novel framework for damage detection and retuning of a Pendulum Tuned Mass Damper (PTMD) addressing effects of stochasticity via mean-square equations and establishing rapid change detection. The framework was made possible via a Stochastic Differential Equation (SDE) formulation of the equations of motion considering a two de...
This paper describes the full-scale testing of a 6.0 m long by 2.0 m wide BladeBridge at the Creagh quarry in Draperstown, Northern Ireland in May 2023 by the ReWind Network. The bridge was constructed on site in April 2022. Preparations for the full-scale testing began soon after the construction was completed. The testing plan was developed in co...
One of the crucial steps in structural health monitoring (SHM) is damage diagnosis based on features extracted from high-dimensional response signals, which are often under uncertain conditions. These uncertainties occur due to noisy ambient excitation, environmental and operational variation (EOV), and measurement conditions. Numerous approaches a...
The combination of tight maintenance budgets and aging railway systems draw attention to the urgent need for cost-effective and efficient approaches to monitor and detect damages in railway systems. Structural Health Monitoring (SHM) has been used by many researchers in railway systems to evaluate the health condition of railway assets. However, it...
During seismic ground shaking, the motion of a soil–pile system is different from that of the free field due to seismic soil–structure interaction (SSI). Kinematic soil–pile interaction is known to cause significant filtering of the ground motion, resulting in the foundation input motion (FIM) differing from the free-field ground motion. In certain...
This paper proposes a synaptic Q-learning algorithm, for the classical cartpole control problem where the Bell-man equations are incorporated at the synaptic level. This enables the iterative evolution of the network topology as a directed graph during training. Topology evolution, in conjunction with mixed-signal computation, leverages the optimiz...
There exist extensive studies on periodic and random perturbations of various smooth maps investigating their dynamics. Unlike smooth maps, non-smooth maps are yet to be studied extensively under a stochastic regime. This paper presents a stochastic piecewise-smooth map derived from a simple inductorless switching circuit. The stochasticity is intr...
This review focuses on the definitions, modalities, applications, and performance of various aspects of digital twins (DTs) in the context of transmission and industrial machinery. In this regard, the context around Industry 4.0 and even aspirations for Industry 5.0 are discussed. The many definitions and interpretations of DTs in this domain are f...
This work experimentally addresses damage calibration of an unmanned aerial vehicle in operational condition. A wide range of damage level and types are simulated and controlled by an electric motor via pulse width modulation in this regard. The measurement is carried out via established protocols of using a piezo-patch on one of the 8 arms, utilis...
Bubble plumes play a significant role in the air–sea interface by influencing processes such as air–sea gas exchange, aerosol production, modulation of oceanic carbon and nutrient cycles, and the vertical structure of the upper ocean. Using acoustic Doppler current profiler (ADCP) data collected off the west coast of Ireland, we investigate the dyn...
Wind turbine blades are normally exposed to significant dynamic loads over their lifetime, including extreme conditions. This can lead to several types of damages such as cracking and delamination. Monitoring the structural condition of the blades to detect damages before they become catastrophic can be important. In recent years, the concept of da...
Reducing the Operation and Maintenance (O&M) costs of Wind Farms can substantially contribute towards adopting environmentally sustainable and cost effective energy sources. O&M costs in Wind Turbines can account up to 50% of the Turbine’s whole life cycle, with the majority of it being the frequent manual inspection needed for Wind Turbine Blades...
In this presentation, a new approach based on Simo-Reissner Beam theory was introduced as an OpenFOAM Restraint Library. This beam theory, in essence, can solve problems with large displacements, which makes it a great tool in simulating mooring lines as beams, which, due to the nature of extreme waves, makes the beam have a non-linear and large di...
This study quantifies the vibration levels emitted by neonatal incubators and analyses the impact of equipment age, mattress types and human behaviour on the vibration levels. A comprehensive dataset of vibration measurements have been recorded and have been compared to the ‘ISO 2631-1:1997 Mechanical vibration and shock’ comfort rating scale. The...
Failure of mechanically stabilized earth (MSE) retaining walls is attributed mainly to excessive displacement of the wall. The wall is permanently displaced when the earthquake motion exceeds its yield acceleration. Determining the permanent displacement of the MSE wall is complex, as the response of the wall is influenced by earthquake characteris...
Wind turbine blades are normally exposed to significant dynamic loads over their lifetime, including extreme conditions. This can lead to several types of damages such as cracking and delamination. Monitoring the structural condition of the blades to detect damages before they become catastrophic can be important. In recent years, the concept of da...
This paper presents an adaption of the finite-element based beam-to-beam contact interactions into a finite volume numerical framework. A previous work of the same authors, where a cell-centred based finite volume implementation of geometrically exact nonlinear Simo–Reissner beams was developed, is used as an underlying mathematical model. An impli...
Knowledge of the directional distribution of a wave field is crucial for a better understanding of complex air–sea interactions. However, the dynamic and unpredictable nature of ocean waves, combined with the limitations of existing measurement technologies and analysis techniques, makes it difficult to obtain precise directional information, leadi...
Achieving Net Zero emissions target is driving up the need for offshore wind as an alternate energy source. Ireland has the capacity to produce upwards of 30GWof power through offshore wind alone. Wind resource assessments are extremely vital in determining the long term trends of a site. The instruments used for this often suffer breakdowns or mis...
Objectives: This study: (i) quantified the typical noise levels in an Irish neonatal intensive care unit (NICU) and compared the values to recommendations by the American Academy of Paediatrics (AAP) and the European Standards for Care for Newborn Health (EFCNI) and to occupational exposure limit value (ELV) and exposure action values (EAVs); and (...
This paper analyzes the dynamics and energy harvesting of a resonantly excited single-degree-of-freedom linear system with an array of pendulums coupled by springs as absorbers. Energy generation along with vibration reduction gives added advantage of generating sufficient electrical energy to powerup portable electronics. Energy harvesting convert...
This paper presents a study on water pipeline leak detection using organic glycineenergy harvesting sensors. The analysis involves examining open circuit voltageswith recurrence quantification analysis (RQA), complexity measures, and neuromorphiccomputing techniques. Time-dependent un-thresholded recurrence plotsreveal nonlinear characteristics in...
This study proposes the new condition monitoring concept of using features in the measured rotation, or ‘pitch’ signal, of a crossing vehicle as an indicator of the presence of foundation scour in a bridge. The concept is explored through two-dimensional vehicle–bridge interaction modelling, with a reduction in stiffness under a pier used to repres...
Fragility estimates in wind turbine towers have been investigated but the the effect of damping on fragility has not been studied. While damping can often be small, it can come from different sources for a wind turbine. This paper demonstrates that even for small levels of equivalent viscous damping, a combination of sources can have a significant...
In this study, we introduce and investigate a new class of split inverse problems, comprising a multidimensional parameter of evolution, which we call multidimensional split variational inequality problem with multiple output sets. To demonstrate its applicability, we formulate the equilibrium flow of multidimensional traffic network models for an...
Operations and maintenance (O&M) of floating offshore wind turbines (FOWTs) require regular inspection activities to predict, detect, and troubleshoot faults at high altitudes and in harsh environments such as strong winds, waves, and tides. Their costs typically account for more than 30% of the lifetime cost due to high labor costs and long downti...
The present work offers a comprehensive overview of methods related to condition assessment of bridges through Structural Health Monitoring (SHM) procedures, with a particular interest on aspects of seismic assessment. Established techniques pertaining to different levels of the SHM hierarchy, reflecting increasing detail and complexity, are first...
There exist extensive studies on periodic and random perturbations of various continuous maps investigating their dynamics. This paper presents a random piecewise smooth map derived from a simple inductor-less switching circuit. The bifurcation parameter is bounded and randomly selected from a stationary distribution. Due to the stochasticity inher...
Extreme wave impacts on coastal infrastructure, including bridges, is a growing problem. Highest energy events are difficult to study because direct observations in real time are almost impossible. Also the non-linear dynamics are difficult to model or to reproduce in scaled experiments. Coastal boulder deposits incorporat-ing megagravel (y axis >4...
Froude scaling for Floating Offshore Wind Turbine (FOWT) platforms is typical for understanding and interpreting their behavior and subsequent designs for testing in wave basins. Despite its popularity, the variability and uncertainty of the kinetic responses of such floating structures as a function of scaling require more attention. This work add...
Investigating floating structures affected by ocean waves using computational fluid dynamics (CFD) models has grown in popularity, particularly for installing floating offshore wind turbines.
There has been tremendous progress in this area, including recent studies such as MoorDyn and Moody, which proposed high-fidelity models for mooring line dyna...
A presentation of my PhD research to date, made at the Wind Energy Science Conference 2023 in Glasgow.
This study investigates the bifurcation behaviour of wake-induced vibro-impacting systems considering fluid-structure interaction (FSI). The primary structure and the near wake dynamics are modelled as a harmonic oscillator a Van der Pol oscillator, respectively, and are weakly coupled to each other. A non-deformable barrier obstructing the motion...
This study investigates the bifurcation behaviour of wake-induced vibro-impacting systems considering fluid-structure interaction (FSI). The primary structure and the near wake dynamics are modelled as a harmonic oscillator a Van der Pol oscillator, respectively, and are weakly coupled to each other. A non-deformable barrier obstructing the motion...
The initial design phase for offshore wind farms does not require complete geotechnical mapping and individual cone penetration testing (CPT) for each expected turbine location. Instead, background information from open source studies and previous historic records for geology and seismic data are typically used at this early stage to develop a prel...
Naturally occurring systems often have inherent uncertainties and often evolve on complicated smooth and differentiable hypersurfaces that are not necessarily Euclidean. The dynamics of such systems can be potentially described using a stochastic Hamiltonian formulation on differentiable manifold. Solution of these stochastic Hamiltonian systems us...
An Adomian decomposition based mathematical framework to derive the mean square responses of nonlinear structural systems subjected to stochastic excitation is presented. The exact mean square response estimation of certain class of nonlinear stochastic systems is achieved using Fokker–Planck-Kolmogorov (FPK) equations resulting in analytical expre...
This paper presents the first implementation of a spiking neural network (SNN) for the extraction of cepstral coefficients in structural health monitoring (SHM) applications and demonstrates the possibilities of neuromorphic computing in this field. In this regard, we show that spiking neural networks can be effectively used to extract cepstral coe...
Lifetime performance requirements for safety and operations of wind turbines is very important for its competitiveness and further uptake. While significant novelties are observed around the development of new turbines, we are also grappling with challenges related to lifetime performance. On the other hand, new materials, sensors, and analysis met...
Ambitious targets have been set for offshore wind generation by countries aiming to reduce carbon emissions. Floating wind farms are an essential component of the wind energy industry, as wind turbines grow bigger and placed in deeper waters. Mooring and anchoring systems are key to the stability of floating offshore wind turbines (OWT). Anchoring...
Many authors have reported the use of deep learning techniques to model wind power forecasts. For shorter-term prediction horizons, the training and deployment of such models is hindered by their computational cost. Neuromorphic computing provides a new paradigm to overcome this barrier through the development of devices suited for applications whe...
There are a large number of time domain, frequency domain and time-frequency signal processing methods available for univariate feature extraction. However, there is no consensus in SHM on which feature, or feature sets, are best suited for the identification, localisation and prognosis of damage. This paper attempts to address this problem by prov...
This work proposes an Itō calculus-based mathematical framework for the optimal design of a nonlinear passive control arrangement. Traditional numerical methods make use of ordinary differential integration schemes to study such nonlinear systems, thereby failing to account for the stochastic nature of the input excitation. Furthermore, such integr...
This study investigates the concept that when localized bridge superstructure damage is present, the weights of passing vehicles inferred from a rotation-based bridge weigh-in-motion (B-WIM) system will deviate from those predicted by a strain-based B-WIM system. Rotation measurements were gathered from a 5.4-m simply supported laboratory model bri...
Mechanical vibrations occur in the operation of most technical systems [...]
At the present time, new types of data are collected at a turbine level, and can be used to enhance the skill of short-term wind power forecasts. In particular, high resolution measurements such as wind power and wind speed are gathered using SCADA systems. These data can be used to build turbine-tailored forecasting models, but at a higher computa...
The vibration and acoustic signals collected from rotating machinery are often non-stationary and aperiodic, and it is a challenge to post-process and extract the defect sensitive health indicators. In this paper, we demonstrate how the estimated Hurst exponent of such measured data can be advantageous for analyzing non-stationary and aperiodic dat...
There is an upwards trend of applying deep learning to model wind power forecasts. The modelling and training of these architectures may take many computational resources, hindering the possibility of implementing such algorithms for shorter term prediction horizons. Emerging computational architectures such as neuromorphic computing have the poten...